Summary

Description

An intertidal barnacle with six coarsely ridged wall plates, a kite-shaped opercular opening, and a membranous base. The rostral plate is relatively narrow and plates are of roughly equal size. The rostral plate is not fused with rostrolaterals. The tissue inside the opercular aperture is blue (paler than in Chthamalus stellatus) with brown and black markings. Usually conical in shape, however when crowded may become tubular. It reaches a maximum diameter of approximately 14 mm, depending on habitat, food availability and level on shore.

Recorded distribution in Britain and Ireland

A warm-water species recorded on the south and west coasts of Britain as far north as Orkney and along the Scottish east coast south to Aberdeen. The Isle of Wight is its eastern limit in the English Channel. It is relatively abundant on Irish coasts.

Global distribution

Crisp et al. (1981) noted that its distribution extends through the western and eastern Mediterranean and down the north African coast to Mauritania.

Depth range

Identifying features

The joint between the terga and scuta crosses the centre line less than one third of the way down towards the rostrum.

Tissue inside opercular aperture is usually blue/pale blue with brown and black markings.

Junction between terga and scuta is concave towards rostral plate.

Shell base is membranous.

Additional information

Before 1976 Chthamalus montagui was considered a variety of Chthamalus stellatus, but in 1976 was identified as a distinct species due to differences in its vertical zonation on the shore and morphology, particularly in the shape of the opercular plates, setation of the smaller cirri, the more sheltered locations in which it was found and its different pattern of zonation (Southward, 1976).

Biology information

Feeding Chthamalus stellatus / Chthamalus montagui generally feed on small plankton. They can consume diatoms, but were found not to grow under a regime dominated by diatoms (Barnes & Barnes, 1965). Normal feeding of chthamalids involves a cirral beat. This cirral beat is also noted to be a respiratory mechanism (Anderson & Southward, 1987). However, in high wave exposure they tend to hold their cirri out stiffly against the water current for a long period of time, retracting when food is captured (Crisp, 1950). Barnacles living in wave exposed conditions may benefit from this passive suspension feeding habit where cirral beating and consequent energy expenditure are minimised (Crisp, 1950).
Rates of cirral beat decrease with age and size, but increase with temperature (Anderson & Southward, 1987). Green (1961) reported that barnacles higher up on shore had a higher cirral beat frequency than those at lower levels. However, Southward (1955; 1964(b)) found no similar trends.
Southward (1955) found that there was no cirral beat of Chthamalus stellatus / Chthamalus montagui in still water and that cirral beating was only induced at a current of approximately 10 cm / sec. The cirral beating frequency is also related to temperature, shown by experiments by Southward (1955). Chthamalus stellatus / Chthamalus montagui barnacles kept at a temperature of 0 °C did not react to touch after an hour. He also found that they remained inactive at a temperature up to 5 °C. Between 5 and 30 °C there was a linear increase to 10 beats every 10 seconds. This slowly declined above 33 °C and dropped rapidly at 36 °C. Although the species resisted coma above a temperature of 40 °C, all cirral beating ceased at 37.5 °C.

Respiration
Sessile barnacles have a pair of gills: pleats of the mantle wall, attached to the mantle cavity (Stubbings, 1975). Rainbow (1984) also stated that the cirri might also play an important role in respiration. There is usually a slow respiratory pumping beat, with varied emergence of the cirri.

Moulting
Barnacles need to moult in order to grow. Feeding rate and temperature determine the frequency of moulting. Moulting does not take place during winter when phytoplankton levels and temperatures are low (Crisp & Patel, 1960).

Growth
Once the barnacle is fixed in place it is unable to detach again (Crisp, 1955). All species grow faster in early life and slower in later life, and chthamalids tend to become tubular when crowded (Southward & Crisp, 1965). The growth rate varies with a variety of biological and environmental factors, including current flow, orientation with respect to current, food supply, wave exposure, shore height, surface contour, and intra- or inter-specific competition. Growth in Chthamalus spp. takes place along the whole internal surface of the one layered plates (Bourget, 1977). The growth rate for Chthamalus stellatus / Chthamalus montagui has been reported by Barnes (1956; Crisp & Bourget (1985) as between 10 - 55 µm per day (relatively slow) in the linear phase. Crisp (1950) noticed that Chthamalus stellatus / Chthamalus montagui reached a maximum size of 0.2 to 1.4 cm. Chthamalus stellatus / Chthamalus montagui was found to have a lower growth rate than many other species of barnacles (Relini, 1983). The species reached a basal diameter of 2-2.5 mm in 3 months, 3.5-4 one year later, up to 8 mm in the 2nd year of growth, but generally no more than about 5-6 mm (Relini, 1983). Sometimes a decrease in size was noticeable, due to abrasion. This low growth rate was found to be associated with a low metabolic rate, or low oxygen consumption, by Barnes & Barnes (1965).

Parasites and epizoites
Healy (1986, in O'Riordan et al., 1992) observed the parasitic isopod, Hemioniscus balani in Chthamalus stellatus and Chthamalus montagui in Ireland, although it was never present in Lough Hyne populations. However, Southward & Crisp (1954) found that although it attacks and sterilises Semibalanus balanoides individuals, it does not normally attack chthamalids on British shores.

Further Information

The dog whelk, Nucella lapillus, feeds on barnacles. The species of Chthamalus spp. are less at risk from dogwhelks due to their smaller size in comparison with Semibalanus balanoides and often higher position on the shore. Other predators which pull shells or cirri of barnacles off the rock, include crabs, amphipods, shore fish such as shanny Lipophrys pholis, and sometimes herring gulls (Moore & Kitching, 1939). Another possible predator is the polychaete, Eulalia viridis (Moore & Kitching, 1939). Chthamalus spp. is also known to be displaced by Patella spp. and smothered by Mytilus spp. and algae at lower shore levels (Moore & Kitching, 1939).

Gubbay (1983) showed that Chthamalus montagui could withstand a compressive force of 42 N and a much lower tensile force of 7.4 N, and that a membranous base adhered to the substrate better than a calcified base.

In order to protect themselves from changes in temperature/desiccation and a lowering of salinity, intertidal barnacles are usually able to close their aperture tightly (Moore & Kitching, 1939)

Habitat Information

Geographical distribution

Crisp et al. (1981) have described the distribution of Chthamalus stellatus and Chthamalus montagui. Chthamalus montagui occurs all around the western seaboard of Britain and all around Ireland. It is absent from part of Liverpool Bay. It occurs in Orkney but not Shetland and extends south down the east coast of Scotland to Aberdeen. On the east coast is more or less continuous, extending from the north of Scotland, along the west coasts of Britain and along all coasts of the Irish Sea.

Records detailing its worldwide distribution are limited, but it is probably that their range extends further south to Mauritania, through western and eastern parts of the Mediterranean Sea. It is rare or absent from offshore islands. It is common in the northern Adriatic and occurs at locations in the Aegean and Black Seas.

Vertical distribution

Chthamalus montagui is dominant over Chthamalus stellatus in more sheltered sites (Southward, 1976; Crisp et al., 1981; Burrows et al., 1992). Where their distributions overlap Chthamalus montagui has a greater vertical distribution above that of Chthamalus stellatus (Burrows et al., 1992) and, while Chthamalus montagui is more common between MHWS & MHWN, Chthamalus stellatus is abundant lower down at MTL and below (Pannacciulli & Relini, 2000). Near its northern limit in Scotland Chthamalus montagui is limited to a narrow band at the top of the shore due to competition with Semibalanus balanoides (Kendall & Bedford, 1987), and the influence of lower temperatures. Poor settlement of Chthamalus spp. also usually occurs. The higher the species occurs up on the shore, the more resistant to desiccation influences they tend to be (Southward, 1955b).

Physical factors such as exposure to seawater, desiccation and poor food supply limit the distribution of barnacles on the upper shore, whereas competition for space, predation and strong wave action limit the distribution at low and mid shore levels (Pannacciulli & Relini, 2000).

The distribution of Chthamalus spp. is not affected by small increases in algal cover. However, rapid increases to 100 % can lead to a massive decline in barnacle populations, declining to almost zero in a year or two (Southward, 1991). Hawkins & Hartnoll (1982) found that the lower shore level limit was controlled by the presence of algal turf.

Substratum preference

Barnacles attach themselves to hard, rough surfaces and are rarely found on chalk cliffs (Moore & Kitching, 1939). Moore & Kitching (1939) also suggested that this may be because the surface is smooth, washed away easily, or too porous (making it possible to be dried out from below).

Temperature dependence / competition

Chthamalus spp. are warm water species, with their northern limit of distribution in Britain. They tend to be more tolerant to temperature increases and desiccation than Semibalanus balanoides. Southward (1976) found that in Cornwall and Devon, where the barnacle is common, it dominates the upper half of the barnacle zone.

Chthamalus spp. prefer warm temperatures, whereas Semibalanus balanoides prefers low temperatures. This is reflected by the changes in their distribution with changes in climate. For example, in the severe winter of 1962-63 Chthamalus populations declined (Southward, 1967) while Semibalanus balanoidesincreased, and in the temperature rise of 1988-89 the trend was reversed (Southward, 1991). Long term trends are also evident. A decline in Chthamalus populations and an increase in Semibalanus balanoides occurred between 1962 and 1980, corresponding with a temporary decrease in sea temperatures (Southward, 1991). Since 1981 there has been a general increase in Chthamalus (Southward, 1991), maybe corresponding with gradual climate warming. Southward & Crisp (1954) noted that in 1948-51, during high temperatures in the British Isles Chthamalus dominated over Semibalanus balanoides, and during 1951-52, during lower temperatures there was a resurgence of Semibalanus balanoides. Southward (1991) noted a two year phase lag between temperature trends and changes in barnacle abundance in Plymouth.

Chthamalus spp. are more abundant in waters where the mean temperatures are above 10 °C for several months of the year (Southward, 1955b).

Larval characteristics

Life history information

Before 1976 there was no distinction between Chthamalus stellatus and Chthamalus montagui. Since 1976 the existence of two separate species was recognised (Southward, 1976). Therefore, papers pre-1976 on Chthamalus stellatus have been recorded as for both Chthamalus stellatus and Chthamalus montagui, below.

Fertilization

Sexual maturity of Chthamalus montagui was attained at a rostro-carinal diameter of 4.4.5-6.4 mm (O'Riordan et al., 1992). Chthamalus montagui is able to breed in its first year (Burrows, 1988; Southward & Crisp, 1954), after 9 to 10 months of settlement (Southward & Crisp, 1954). Sperm is activated by the oviducal gland and transferred to the oviducal sac via the penis of a neighbouring barnacle (Barnes, 1989). The barnacle penis is substantially longer than the body and is capable of searching an area around the adult to find a receptive 'functional female' (Rainbow, 1984).

Barnacles generally reproduce by cross-fertilization, but Chthamalus has been shown to self-fertilize when isolated (Barnes & Barnes, 1958; Barnes, 1989); this usually occurs high up on shore. However, it has been noted that in self-fertilized individuals oviposition is delayed (Barnes & Barnes, 1958; Barnes, 1989) and the resulting eggs can be slightly abnormal and are considered less viable (Barnes, 1989). Egg masses (egg lamellae) are brooded in the mantle cavity (O'Riordan et al., 1995; Barnes, 1989).

Breeding season

Southward (1978) suggested that Chthamalus montagui breeds one to two months later than Chthamalus stellatus. However, Crisp et al. (1981) found little difference in SW Britain, with the main breeding peak in June/July and August. Throughout the breeding season most individuals produce several broods (Burrows et al., 1992; O'Riordan et al., 1992), with a small percentage of the population remaining reproductively active throughout the year (O'Riordan et al., 1995); Barnes, 1989). After maturation of each brood ovarian and penis re-development takes place (O'Riordan et al., 1995; Barnes & Barnes, 1965; Burrows, 1988; Anderson, 1994).

According to Hines (1978) temperature and food availability are the main factors controlling the duration of the breeding season and the embryonic development rate of other Chthamalus species. In fact, Burrows (1988, in Kendall & Bedford, 1987) found the onset of the breeding season to be correlated with a sea temperature of 10 °C or above (Burrows et al., 1992). Southward & Crisp (1956) noted that the interval between broods in Chthamalus stellatus and Chthamalus montagui became shorter at higher temperatures.

The onset of the breeding season was noticed by Crisp (1950) to spread up the shore level over several months. Brooding in Aberystwyth was noted to be in May/June to August (Kendall & Bedford, 1987), with approximately 80 % containing a naupliar mass. Cyprid settlement occurred in late July to early September at a sea temperature of 15.3 to 18.8 °C (Kendall & Bedford, 1987). In northern Spain the brooding period tends to be longer, between April and early October, with 30 % containing a naupliar mass (Kendall & Bedford, 1987).

The breeding period, period of larval settlement and density of recruits are all reduced near the northern limits of its distribution. Crisp (1950) suggested that for Chthamalus montagui and Chthamalus stellatus in the United Kingdom, breeding commenced earlier with decreasing longitude and easterly longitude. Breeding of Chthamalus stellatusand Chthamalus montagui usually takes place earlier in the year in continental Europe than in the British Isles (Relini & Matricardi, 1979; Relini, 1983; Miyares, 1986, all in O'Riordan et al., 1995). In the Mediterranean the breeding season usually occurs in July and August (Mizrahi & Achituv, 1990, in O'Riordan et al., 1995).

Experiments by O'Riordan et al. (1995) showed that in their first year Chthamalus stellatus and Chthamalus montagui breed once or more, and more than once thereafter.

Embryonic development

In both Chthamalus stellatus and Chthamalus montagui it took approximately 23 days for embryos to develop completely in vivo at 15 °C (Burrows et al., 1992; Burrows, 1988, in Kendall & Bedford, 1987). Chthamalus montagui will only breed if temperatures exceed 15 degrees C (Patel & Crisp, 1960).

Recruitment and lifespan

Towards the northern limits of the species distribution annual recruitment is low (Kendall & Bedford, 1987) and individuals have an increased longevity (Lewis, 1964). The normal lifespan of Chthamalus stellatus / Chthamalus montagui at mid-shore level is considered to be approximately 2-3 years (Southward & Crisp, 1956). However, growth is more rapid and the mortality rate is greater lower down on the shore (Southward & Crisp, 1956).

Fecundity

(Burrows et al., 1992) found that the number of eggs per brood for Chthamalus montagui ranged between 1,030 to 1803 in Britain, depending on body size and weight. It was also noted by (Burrows et al., 1992) that the fecundity generally increased with lower shore levels colonized, with estimations of 1-2 broods per year at high shore levels, 2 to over three at mid shore levels, and over 2 to over 4 at low shore levels.

This MarLIN sensitivity assessment has been superseded by the MarESA approach to sensitivity assessment. MarLIN assessments used an approach that has now been modified to reflect the most recent conservation imperatives and terminology and are due to be updated by 2016/17.

Physical pressures

Barnacles are permanently attached to hard rough surfaces. Therefore, loss of substratum due to activities such as spoil dumping or land claim will result in loss of individuals in the area. If suitable substrata remains within the area, colonization of juvenile barnacles is possible. Intolerance is assessed as high. Recoverability is likely to be moderate (see Additional Information section below).

Chthamalus stellatus / Chthamalus montagui have been shown to be relatively unaffected by smothering by oil. Monterosso (1930) showed experimentally that the species can survive complete smothering by petroleum jelly for approximately two months, by respiring anaerobically. Complete smothering caused by the Torrey Canyon oil spill yielded similar results; A few Semibalanus balanoides died, yet Chthamalus stellatus / Chthamalus montagui seemed unaffected, while at Booby's bay more than 90 % had managed to clear an opening in the oil film (Smith, 1968). Although oil had very little effect on individuals, it is likely that smothering by sediment can clog breathing apparatus. Recruitment to the smothered area will also be reduced. Therefore intolerance is assessed as intermediate. Recoverability is likely to be high (see Additional Information section below).

Barnacles are likely to be able to tolerate a slight increase in siltation. A large increase in siltation to 100 mg/l for one month is may block breathing apparatus and impose an energetic cost of cleaning the gills. Intolerance is therefore, assessed as low. Recoverability is likely to be very high as feeding and respiratory structures are likely to be clear of particles within a short space of time.

Chthamalus montagui is a warm water species, with its northern limit of distribution in Britain. It tends to be more tolerant to desiccation than Semibalanus balanoides. The higher the species occurs up on the shore, the more resistant to desiccation influences they tend to be (Southward, 1955b). Cracks and crevices offer further protection from desiccation. Southward (1958) reported an internal temperature of 28.8 °C in an air temperature of 13.7 °C.
Chthamalids are prevented from growing higher up the shore due to their desiccation tolerance. Therefore, an increase in the level of desiccation would cause a depression in the upper limit of the species vertical distribution. A decrease in the level of desiccation may elevate their upper limit. Therefore, intolerance is assessed as low. Recoverability is likely to be very high (see Additional Information section below).

According to Hines (1978) temperature and food availability are the main factors controlling the duration of the breeding season and the embryonic development rate in other species of Chthamalus. With an increase in emergence, the period of time covered by the water would decrease, and the time available for feeding and breeding would also decrease. This is likely to reduce the growth rate and annual recruitment. There is also likely to be a shift downwards on the shore due to competition with Semibalanus balanoides. Intolerance is assessed as intermediate. Recoverability is likely to be high (see Additional Information section below).

Barnacle populations are likely to be tolerant of an decrease in emergence. According to Hines (1978) temperature and food availability are the main factors controlling the duration of the breeding season and the embryonic development rate in other species of Chthamalus. With a decrease in the emergence regime, the feeding time and breeding possibilities are likely to increase. Adults of Chthamalus stellatus/ Chthamalus montagui can survive permanent submersion (Barnes, 1953). However, competition between Semibalanus balanoides is likely to play an important role in the changes in the species distribution. It is likely that the distribution of Chthamalus montagui will move further up the shore, with no noticeable difference in the range. Intolerance is assessed as low. Recoverability is likely to be very high (see Additional Information section below).

An increase in water flow rate is likely to lead to higher growth rates and annual recruitment. Intolerance is assessed as low. Recoverability is likely to be very high (see Additional Information section below).

A decrease in the water flow rate is likely to lead to a decrease in growth rate and annual recruitment. Intolerance is assessed as low. Recoverability is likely to be very high (see Additional Information section below).

Chthamalus montagui would be favoured by an increase in temperature based on the following information:

Chthamalus montagui is a warm water species, with its northern limit of distribution in Britain. It tends to be more tolerant to temperature increases than Semibalanus balanoides.

Southward (1958) reported an internal temperature of 28.8 °C in an air temperature of 13.7 °C. Therefore, a slight increase in temperature can lead to a much larger increase in temperature inside the barnacle during exposure to air and the sun.

Since 1975 there has been a general increase in the abundance of Chthamalus montagui and Chthamalus stellatus (Southward, 1991), perhaps corresponding with gradual climate warming. Southward (1991) noted a two year phase lag between temperature trends and changes in barnacle abundance in Plymouth.

Chthamalus sp. is most abundant in waters where the mean temperatures are above 10 °C for several months of the year (Southward, 1955b). According to Hines (1978) temperature and food availability are the main factors controlling the duration of the breeding season and the embryonic development rate whilst Burrows (1988, in O'Riordan et al., 1995) found the onset of the breeding season to be correlated with a sea temperature of 10 °C or above.

Southward & Crisp (1956) noted that the interval between broods in Chthamalus stellatus and Chthamalus montagui became shorter at higher temperatures.

Chthamalus montagui will only breed in temperatures above 15 degrees C (Patel & Crisp, 1960). Therefore intolerance to an increase in temperature is likely to increase reproduction, the rate of larval and embryonic development and, therefore, recruitment.

At an upper temperature limit of 20 - 21 °C in the sea and 24 - 25 °C in the air reproductive activity decreased (Barnes, 1992). Intolerance is assessed as tolerant* in the British Isles. Recoverability is likely to be very high (see Additional Information section below).

During the severe winter of 1962-63, over the majority of the species range, chthamalids were able to withstand the cold. However, greater mortalities were noted to occur a month or two after the coldest weather (Crisp, 1964). Chthamalid populations declined while Semibalanus balanoides increased (Southward, 1967). A decline in Chthamalus sp. populations and an increase in Semibalanus balanoides occurred between 1951 and 1975, corresponding with a decrease in sea temperatures (Southward, 1991). Southward & Crisp (1954) noted during 1951-52, during lower temperatures there was a resurgence of Semibalanus balanoides. (Southward, 1991) noted a two year phase lag between temperature trends and changes in barnacle abundance in Plymouth.Chthamalus sp. is more abundant in waters where the mean temperatures are above 10 °C for several months of the year (Southward, 1955b). According to Hines (1978) temperature and food availability are the main factors controlling the duration of the breeding season and the embryonic development rate. In fact, Burrows (1988, in O'Riordan et al., 1995) found the onset of the breeding season to be correlated with a sea temperature of 10 °C or above (Burrows et al., 1992). Southward & Crisp (1956) noted that the interval between broods in Chthamalus stellatus and Chthamalus montagui became shorter at higher temperatures. Chthamalus montagui will only breed in temperatures above 15 degrees C (Patel & Crisp, 1960).
A decrease in temperature is therefore likely to result in greater mortality of Chthamalus species, and a resurgence in Semibalanus balanoides. Recruitment is also likely to decline. Intolerance is assessed as high. Recoverability is likely to be low (see Additional Information section below).

Barnes & Barnes (1968) found that in high suspended solids and low salinity there was a decrease in the number of eggs per brood of Chthamalus stellatus / Chthamalus montagui. Fecundity in protected areas such as harbours is usually lower, possibly due to increased turbidity (Barnes, 1989). Intolerance is assessed as intermediate. Recoverability is likely to be moderate (see Additional Information section, below.)

Chthamalus montagui colonizes exposed to moderately exposed rocky shores. A decrease in wave exposure below 'moderately exposed' is likely to result in a proportion of the population dying. A decrease in the level of wave exposure may also cause a shift in the community towards fucoid algae, which prevent barnacle larvae settlement. Intolerance is assessed as intermediate. Recoverability is likely to be moderate (see Additional Information section below).

Cracks and crevices offer protection from some abrasion but the majority of barnacles are on open rock surfaces and liable to be crushed by abrasive forces such as cobbles moving in wave action or vessel strandings. Small abrasive forces, such as erosion from suspended sediment, has been noted to cause a decrease in barnacle size (Relilni, 1983). On a larger scale, Gubbay (1983) showed that Chthamalus montagui could withstand a compressive force of 42 newtons (N) and a much lower tensile force of 7.4 N, perhaps equivalent to trampling pressure. Therefore, intolerance is assessed as intermediate. Recoverability is likely to be high (see additional information below).

Once the barnacle is fixed in place it is unable to attach again (Crisp, 1955). Intolerance to displacement is therefore assessed as high. Recoverability is likely to be moderate (see Additional Information section below).

Chemical pressures

Barnacles have a low resilience to chemicals such as dispersants, dependant on the concentration and type of chemical involved (Holt et al., 1995). They are less intolerant than some species (e.g. Patella vulgata) to dispersants (Southward & Southward, 1978). In areas which where large amounts of detergents had been used, there was much greater mortality, and in Kynance cove the population was wiped out completely (Smith, 1967). However, the barnacle population suffered indirectly as a result of the mass mortality of grazers. The resultant bloom of algae, and growth of fucoids, within 6 months, grew over and killed surviving barnacles (Hawkins & Southward, 1992). Intolerance to synthetic chemicals is assessed as intermediate. Recoverability is likely to be high (see Additional Information section, below).

Heavy metal contamination

Low

High

Low

Very low

Barnacles accumulate heavy metals and store them as insoluble granules. No information is available as to the effects of heavy metals on Chthamalus montagui, but a larger amount of information was found with respect to a barnacle from the same family, Semibalanus balanoides. It is possible that sensitivities to heavy metals may be similar in both species. Clarke (1947) investigated the intolerance of Semibalanus balanoides to copper, mercury, zinc and silver. He found that 90 percent of barnacles died when held in 0.35 mg/l Cu carbonate for two days. Zinc, mercury and silver killed 90 percent of barnacles in two days at concentrations of 32 mg/l, 1 mg/l and 0.4 mg/l respectively. Pyefinch & Mott (1948) recorded median lethal concentrations of 0.32 mg/l copper and 0.36 mg/l mercury over 24 hours for this species. Barnacles may tolerate fairly high level of heavy metals in nature, for example they are found in Dulas Bay, Anglesey, where copper reaches concentrations of 24.5 µg/l, due to acid mine waste (Foster et al., 1978). Therefore, intolerance to heavy metals is assessed as low. Recoverability is likely to be high (see Additional Information section, below).

Hydrocarbon contamination

Low

High

Low

Moderate

Chthamalus stellatus/ Chthamalus montagui have been shown to be relatively unaffected by smothering by oil (Southward & Southward, 1978; Smith, 1967). Monterosso (1930) showed experimentally that the species can survive complete smothering by petroleum jelly for approximately two months, by respiring anaerobically. Complete smothering caused by the Torrey Canyon oil spill yielded similar results; A few Semibalanus balanoides died, yet Chthamalus stellatus / Chthamalus montagui seemed unaffected (Southward & Southward, 1978; Smith, 1968), while at Booby's Bay more than 90 % had managed to clear an opening in the oil film. On further examination these individuals were found to be in good condition, with no oil present in the gut (Smith, 1967).
However, detergents used to clean up the oil lead to a decline in Chthamalus sp. populations. In areas which where large amounts of detergents had been used, there was much greater mortality, and in Kynance cove the population was wiped out completely (Smith, 1967).Therefore, intolerance is assessed as low. Recoverability is likely to be high (see Additional Information section, below).

Radionuclide contamination

No information

Not relevant

No information

Not relevant

Insufficientinformation.

Changes in nutrient levels

Intermediate

High

Low

Low

Little data exists on the effects of increased nutrients on barnacles. A slight increase in nutrient levels may be beneficial for barnacles by promoting the growth of flagellates. However, Holt et al. (1995) predict that smothering by ephemeral green algae is a possibility under eutrophic conditions. Therefore, intolerance to nutrient levels is assessed as intermediate. Recoverability is likely to be high (see Additional Information section, below).

Barnacles are able to acclimate over a number of days to reduced salinity (Rainbow, 1984; Moore & Kitching, 1939; Foster, 1970). However, the acclimatisation, or closing of the opercular plate is also associated with anaerobiosis and low metabolic activity (Barnes et al., 1963). Barnes & Barnes (1965) found that in high suspended solids and low salinity there was a decrease in the number of eggs per brood of Chthamalus stellatus / Chthamalus montagui. If salinities decrease below 21 psu all cirral activity of barnacles that are normally associated with full salinity coastal waters, ceases (Foster, 1971). Therefore, intolerance to a decrease in salinity is assessed as high. Recoverability is likely to be high (see Additional Information section, below).

Southward (1955) conducted experiments on the relationship of cirral activity in Chthamalus stellatus / Chthamalus montagui, connected with feeding and respiration, to decreased oxygenation, by passing nitrogen through the water at 6 ml per minute at 13 °C. He found that in all cases a decrease in oxygen concentration lead to a decrease in cirral activity and that, after 15 minutes, the mean cirral beat had decreased from 3.1 to 2.9 beats per second. After 30 minutes exposure, cirral beat had completely ceased and the barnacle remained inactive. It was further observed that the scuta and terga remained slightly open with the cirri often protruding.Barnacles have to obtain oxygen from the water through their cirri including by cirral beating in still water. Since cirri stop beating in response to lowered oxygen levels, it seems likely that intolerance will be high. Therefore, intolerance to oxygen levels is assessed as high. Recoverability is likely to be high (see Additional information section, below).

Biological pressures

Healy (1986, in O'Riordan et al., 1992) has observed the parasitic isopod, Hemioniscus balani in Chthamalus stellatus and Chthamalus montagui in Ireland, although it was never present in Lough Hyne. However, Southward & Crisp (1954) found that, although it attacks and sterilises Semibalanus balanoides individuals, it does not attack chthamalids, at least not in the British Isles. Therefore, intolerance is assessed as intermediate. Recoverability is likely to be high (see Additional Information section, below).

The Australasian barnacle Elminius modestus was introduced to British waters on ships during the second world war. The species does well in estuaries and bays, where it can displace Semibalanus balanoides and Chthamalus montagui. The native species are not displaced completely because they out-compete Elminius on exposed shores (Raffaelli & Hawkins, 1999). Intolerance to the introduction of non-native species is assessed as intermediate. Recoverability is likely to be high (see Additional information section, below).

Collection of intertidal algae may damage barnacles by abrasion from trampling. Intolerance to the extraction of other species is assessed as low. Recoverability is likely to be high (see Additional information section, below).

Additional information

Chthamalus montagui is able to breed in its first year (Burrows, 1988, in O'Riordan et al., 1995; Southward & Crisp, 1954), nine to ten months after settlement (Southward & Crisp, 1954). Throughout the breeding season most individuals produce several broods (Burrows et al., 1992; O'Riordan et al., 1992), with a small percentage of the population remaining reproductively active throughout the year (O'Riordan et al., 1995; Barnes, 1989).

Barnes, H., 1956. The growth rate of Chthamalus stellatus (Poli). Journal of the Marine Biological Association of the United Kingdom, 35, 355-361.

Barnes, H., Finlayson, D.M. & Piatigorsky, J., 1963. The effect of desiccation and anaerobic conditions on the behaviour, survival and general metabolism of three common cirripedes. Journal of Animal Ecology, 32, 233-252.

Patel, B. & Crisp, D. J., 1960. The influence of temperature on the breeding and the moulting activities of some warm-water species of operculate barnacles. Journal of the Marine Biological Association of the United Kingdom, 36, 667-680.

Patel, B. & Crisp, D.J., 1960. Rates of development of the embryos of several species of barnacles. Physiology and Zoology, 33, 104-119.

Pyefinch, K.A. & Mott, J.C., 1948. The sensitivity of barnacles and their larvae to copper and mercury. Journal of Experimental Biology, 25, 276-298.

Southward, A.J. & Crisp, D.J., 1956. Fluctuations in the distribution and abundance of intertidal barnacles. Journal of the Marine Biological Association of the United Kingdom, 35, 211-229.

Southward, A.J. & Crisp, D.J., 1965. Activity rhythms of barnacles in relation to respiration and feeding. Journal of the Marine Biological Association of the United Kingdom, 45, 161-185.

Southward, A.J. & Southward, E.C., 1978. Recolonisation of rocky shores in Cornwall after use of toxic dispersants to clean up the Torrey Canyon spill. Journal of the Fisheries Research Board of Canada, 35, 682-706.

Southward, A.J., 1955. On the behaviour of barnacles. I. The relation of cirral and other activities to temperature. Journal of the Marine Biological Association of the United Kingdom, 34, 403-432.

Southward, A.J., 1955b. On the behaviour of barnacles II. The influence of habitat and tidal level on cirral activity. Journal of the Marine Biological Association of the United Kingdom, 34, 423-433.

Southward, A.J., 1958. Note on the temperature tolerances of some intertidal animals in relation to environmental temperatures and geographical distribution. Journal of the Marine Biological Association of the United Kingdom, 37, 49-56.

Southward, A.J., 1964b. The relationship between temperature and rhythmic cirral activity in some Cirripedia considered in connection with their geographical distribution. Helgolander Wissenschaftliche Meeresuntersuchungen, 10, 391-403.

Southward, A.J., 1967. Recent changes in abundance of intertidal barnacle in south-west England: a possible effect of climatic deterioration. Journal of the Marine Biological Association of the United Kingdom, 47, 81-85.

Southward, A.J., 1976. On the taxonomic status and distribution of Chthamalus stellatus (Cirripedia) in the north-eastern Atlantic region: with a key to the common intertidal barnacles of Britain. Journal of the Marine Biological Association of the United Kingdom, 56, 1007-1028.

Southward, A.J., 1991. Forty years of changes in species composition and population density of barnacles on a rocky shore near Plymouth. Journal of the Marine Biological Association of the United Kingdom, 71, 495-513.

The information (TEXT ONLY) provided by the Marine Life Information Network (MarLIN) is licensed under a Creative Commons Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales License. Note that images and other media featured on this page are each governed by their own terms and conditions and they may or may not be available for reuse. Permissions beyond the scope of this license are available here. Based on a work at www.marlin.ac.uk